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“Delivery disruption can have large consequences if a pipeline operator has a contractual obligation to keep gas flowing. Shutting down supply to a liquefied natural gas facility could cost such a plant around a hundred million dollars, for example.”

Live repair techniques
DNV GL is a technology leader for live repair. It has lately been involved in many, using various techniques such as welding, epoxy grouted sleeves, Grouted Tees, welded or mechanical sleeves, and pipeline clamps.

Epoxy grouted sleeves involve installing a steel sleeve around a non-leaking pipeline, then introducing a quick-drying end seal before injecting epoxy grout between sleeve and pipe. Grouted Tee is a similar technology but has a branch connection and seal enabling pipeline contents and high pressure to be contained. A single Grouted Tee can isolate a minor leak or encapsulate a damaged or deteriorated branch connection. Multiple Grouted Tees can provide a flow-stop and bypass arrangement to enable replacement of larger sections of pipeline.

Grouting is simple and does not require on-site welding, so full flow can be maintained during repair or intervention. Usage of Grouted Tees has expanded to include repairs on thin-walled and cast iron pipelines, and on subsea pipelines in up to 200 metres (m) of water depth.

“It is worth noting that the total cost of Grouted Tee connections is usually less than traditional, welded Tees at larger diameters, and they also benefit from a 40-year minimum design life compared with the 20 to 30 years that is common for a pipeline,” Venås said.

Tees and sleeves may be welded rather than grouted to a live pipeline, but this requires flow reduction and can increase safety risks. Simple clamps can be used for temporary seals while permanent repairs are designed.

Design standards usually specify heavy wall pipe for sections subject to higher external forces, at road and rail crossings for example. Replacing standard with heavy wall pipe is very expensive if a pipeline has to be decommissioned during repairs, and could even be hazardous when flow is stopped while a bypass is welded into place to isolate a leaking section.[1]

An epoxy grouted sleeve involves zero downtime, can address most onshore pipeline defects, and is one of few repairs suitable for defects in girth welds that join pipes end-to-end around their circumference.

Contact us:

Asle Venås

A novel hyperbaric chamber allowed divers to weld sleeves safely around subsea pipeline in Asia. The chamber anchors to retrievable piles, the pipe is temporarily sealed in, water pumped out, and the repair then made. DNV GL was part of the project organization. Photo: DCN Diving

“Delivery disruption can have large consequences if a pipeline operator has a contractual obligation to keep gas flowing”Asle Venås,

global segment director for pipelines

DNV GL - Oil & Gas

Case study: live repair onshore
DNV GL recently completed the development of modified epoxy repair sleeves for an 80m length of 48 inch (in) diameter, standard wall thickness gas pipeline with a pressure rating of 94 bar at a road crossing at Red Roses in South Wales.

This work was conducted on behalf of the international gas and electricity company National Grid, sole owner and operator of gas transmission infrastructure in the UK. Epoxy sleeves are National Grid’s preferred repair method for defects on all of the company's gas transmission and distribution pipelines.

The Red Roses pipeline reinforcement project was completed for the Welsh government. This encompassed several bends along the 80m length of pipeline in order to protect and increase its
integrity to an equivalent of thick wall pipe. Overlapping of sleeves increased the integrity of each joint, providing complete protection over the full length. The journey from conceptual design to project completion took 15 months.

Compared with a traditional heavy wall pipe section replacement method, savings were estimated to have been GBP40-50 million (USD57-72m). While being the most cost-effective method, the epoxy sleeve option also eliminated a substantial amount of hot work associated with the traditional pipeline replacement method, which significantly reduced the risk to the pipeline and personnel.

“By using the epoxy technology, we avoided a complex and costly diversion, significantly reduced risk and still maintained the gas supply throughout the whole operation,” said Mark Whittaker, project engineer, National Grid. “With the economic necessity of maintaining production and reducing risk, using epoxy sleeves to reinforce pipelines could become increasingly prevalent where operational constraints allow.”

The success of Red Roses, and the infinite length of pipeline that the epoxy sleeve method can cover on a road crossing is now being discussed by the UK’s Institution of Gas Engineers and
Managers for inclusion in future revisions of pipeline standards, as a possible alternative to replacing heavy wall pipe where circumstances allow.

Case study: live repair offshore
Production downtime for pipeline repairs offshore can cost millions of dollars per day in lost revenue, so live repair is attractive here too, even though it is technically challenging.[2]

When a 32in natural gas pipeline leaked offshore earlier in this decade, there was concern that 25% of homes and businesses in a large Asian city could suffer partial power blackouts.

The pipeline operator engaged DNV GL to help assess the situation. The pipeline was temporarily repaired within a week by using an off-the-shelf leak clamp.

However, the operator wanted a permanent repair that could be done with the pipeline live and would last 20–30 years. DNV GL recommended using a type of sleeve (welded stand-off) developed by the company and used during projects in Russia and China. A more familiar solution at the time would have been to install a temporary bypass pipeline to allow the damaged section to be cut out and replaced in a hyperbaric (dry) environment. However, both the pipeline and leak locations in Asia meant this would be too complex, risky, entail a long lead time, and would involve disturbance to gas flow. As part of the project organization, DNV GL contributed technical solutions and added barriers to ensure safety of the live welding operation that enabled use of welded stand-off sleeves.

“We used resources from our large global network of pipeline experts to support our local project management and site team to develop, qualify, design, test and follow up the repair at site,” Venås said. “There was no supply disruption over the 18 months that this novel solution took to complete, and flow rate and pressure were maintained.”

New project tackles cost
To further assist customers such as National Grid and the Asian operator, DNV GL recently launched EC-Pipe, an internally-funded project to help the industry reduce capital and operational expenditure, and to increase efficiency, while maintaining acceptable reliability and safety standards.

Pipeline standard still leads the way 40 years on

DNV-OS-F101, the first global Standard for design, construction and operation of offshore submarine pipelines, was launched first in 1976 and remains one of the few, limit state design codes for pipelines.

Over the past 40 years, it has been used for many high profile projects across the world, such as Langeled and Polarled in the North Sea, Australia’s Wheatstone and Ichthys, and South Stream in the Black Sea. Around 65% of new pipeline projects globally are designed to this risk-based
Standard. It is supported by 14 recommended practices and meets ISO requirements.

“DNV-OS-F101 shows what industry collaboration can achieve regardless of peaks and troughs in market conditions,” said Venås.

“With the economic necessity of maintaining production and reducing risk, using epoxy sleeves to reinforce pipelines could become increasingly prevalent where operational constraints allow”
Mark Whittaker,

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DNV GL prides itself on providing accurate information but makes no claims or guarantees about the accuracy, completeness or adequacy of contents in this publication, and disclaims liability for any errors or omissions. The authors’ views here do not necessarily reflect DNV GL’s views.